Techniques for analyzing or measuring the elemental composition of a substance, such as coal, using X-ray fluorescence (XRF), are well-known in the art. An example of one technique is disclosed in U.S. Pat. No. 6,130,931, the disclosure of which is incorporated herein by reference. While these XRF techniques work extraordinary well for measuring certain elements, such as sulfur, the ability to measure “trace elements” (e.g., vanadium, chromium, manganese, cobalt, nickel, copper, zinc, arsenic, selenium, and molybdenum) has previously been limited to laboratory techniques involving extensive preparation using pulverized samples. For instance, ASTM Standard Test Method D4606 for the determination of arsenic and selenium in coal by the Hydride Generation/Atomic Absorption Method analyzes a 1.0 gram sample of coal pulverized to pass a 250 mm standard sieve. ASTM Standard Test Method D6357 for the Determination of Trace Elements in Coal, Coke, and Combustion Residues from Coal Utilizations Processes by Inductively Coupled Plasma Mass Spectrometry and Graphite Furnace Atomic Absorption Spectrometry analyzes a 0.5 gram sample of coal ash ground to pass 150 μm. The wet chemistry methods dictated by standard laboratory methods are time consuming and can only produce a single analysis in a matter of hours. Turn around time in commercial laboratories is often days or weeks and the analysis is very expensive.
U.S. Pat. No. 5,020,084 to Robertson, which is also incorporated herein by reference, proposes the use of X-ray energy at a level of 100–130 kilo-electron-volts (KeV) to measure a finely divided heavy metal (gold) dispersed in a non-metallic matrix using K emission bands. However, this patent does not mention the use of low energy XRF to measure trace elements, including gold. Moreover, it dismisses L emission XRF techniques as inaccurate. Furthermore, high energy XRF cannot be used to detect the K emission bands of the lighter trace elements with atomic numbers less than or equal to 48 (Cadmium). Thus, the approach taught in the Robertson patent is not a solution to the problems identified in the foregoing paragraph.